Pros

Pro

Performance speed comparable to native C

Pro

Backed by Apple

Pro

Uses LLVM compiler and Obj-C runtime allowing C, Objective-C, Objective-C++ and Swift code to run side by side within a single program

Pro

Inherent parallelism

Pro

Low memory footprint due to reference counting

Pro

Can be used as a Just-In-Time language

Pro

Swift has some clever tricks up its sleeve

Due to having elements of a functional programming language. Things like 'map' and 'filter' for example.

Pro

Works with Apple's Cocoa and Cocoa Touch frameworks

Pro

Modern syntax

Cons

Con

Swift is a moving target

They've released 1.2 so far, and 2.0 is coming soon. Every small update brings adjustments to paradigms (such as how to do type casting) that can be a little frustrating to absorb. Objective C was also constantly updating, however, but not at the same rate these days.